HR: 14:25h
AN: PP13D-02    [Abstracts]
TI: Diurnal Weather Cycles at the Tropical Treeline in the North American Monsoon Region
AU: * Biondi, F
EM: fbiondi@unr.edu
AF: DendroLab, University of Nevada, Dept. of Geography, MS 154, Reno, NV 89557, United States
AB: High elevation atmospheric processes in the North American Monsoon region were investigated using half-hour weather data collected from May 22^nd, 2001 to March 21^st, 2007 at Nevado de Colima, Mexico (19° 35' N, 103° 37' W, 3760 m a.s.l.). After briefly expanding on temporal changes, which were first described by Biondi et al. 2005, I investigate diurnal weather cycles using the entire period of record. During the monsoon, precipitation falls mostly in the afternoon (from 12:00 to 20:00), with a peak around 17:00. Barometric pressure follows a regular wave pattern in all months, with a high at noon in between two lows, one around 5:30 and one between 17:00 and 19:00. Since barometric pressure is higher during the wet season, and the lows are found in all months, the afternoon low is not related to precipitation; rather it may help convective processes during the monsoon season. The diurnal pressure waves correspond to changes in wind speed, but it is unclear if turbulence drives the changes in pressure, as suggested by other authors. In particular, the amplitude of the atmospheric wave is greater in the dry season than in the wet season, in contrast to what was observed at high elevations in the Alps. The diurnal cycle of air temperature shows maxima during the spring, as the increased cloudiness during the summer wet season reduces incoming short wave radiation and its direct outcome, maximum air temperature. The dry season is characterized by greater excursions in air temperature, since the interval between maxima and minima is larger at all hours of the day. Soil temperature (especially the minima) is higher during the wet season, and shows an afternoon peak, most likely related to precipitation. Both minimum and maximum soil temperatures are at their lowest level around noon. Atmospheric vapor and vapor pressure deficit follow opposite patterns, as expected according to the season and the diurnal cycle of precipitation. These data provide a unique baseline for future comparisons, provide a clear example of the value of permanent plots in the portion of the American Cordillera that is affected by the North American Monsoon system, and fill a data gap in tropical treeline environments. From the uncovered patterns and processes, it also follows that better understanding of weather and climate processes is needed for both forecasting and backcasting of regional and global changes in monsoon systems across multiple timescales.
UR: http://woods.geography.unr.edu/dendrosite/mexico.htm
DE: 1620 Climate dynamics (0429, 3309)
DE: 1637 Regional climate change
DE: 1833 Hydroclimatology
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 4914 Continental climate records
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting